If powdered natto bacteria is unavailable, use a pack of natto
Rinse the soy beans and reconstitute overnight for 12 hours in water 3 to 4 times times the amount of soy beans.
Steam the reconstituted soy beans in a pressure cooker for 30 minutes.
Put soy beans into the yogurt maker while still warm, and a mixture of powdered natto bacteria and 1/2 to 1 tablespoon of cooled boiled water, then mix.
Without covering with the inner lid, cover with cheese cloth or a paper towel, and close the lid, leaving a slight gap for air to escape.
Set the yogurt maker to 105F/40C for 24 hours.
When a whitish film forms on the surface and the soy beans are stringy when pulled apart, it's done.
This is how it looks before storing in the refrigerator. Store in a container with a drainboard, if available, and let sit in refrigerator for 1 to 2 days.
Story Behind this Recipe
I want to be able to eat Japanese food whether I'm living in Japan or not. Even if Japanese food is available, it is too expensive, and since the only solution is to make my own, I experimented with several methods and came up with this one.
You can also boil the beans, but it's better when steamed. I steam mine in a stainless steel colander inserted inside a pressure cooker.
For a tasty result, the soy beans should be soft enough to crush with your fingers.